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Abstract

We study random coupling induced crosstalk between groups of degenerate modes in spatially multiplexed optical transmission. Our analysis shows that the average crosstalk is primarily determined by the wavenumber mismatch, by the correlation length of the random perturbations, and by the coherence length of the degenerate modes, whereas the effect of a deterministic group velocity difference is negligible. The standard deviation of the crosstalk is shown to be comparable to its average value, implying that crosstalk measurements are inherently noisy.

The deterministic coupling between members of an LP mode group [9] is not included in B as its effect is assumed to be masked by the presence of the random perturbations which are represented by the second term in the square brackets of Eq. (1). This is consistent with the fact that strong random coupling between the constituent pseudo-modes is observed in experiments.

Strictly speaking the matrices Ul and Uq are independent up to a scalar phase factor that is negligible as compared to the phase difference due to the deterministic wavenumber mismatch.

The quantity that we refer to as the coherence length of the field describes the propagation distance along which the field decorrelates due to the fiber perturbations. It is not related to the coherence length of the light source.

Proc. Natl. Acad. Sci. USA (1)

Other (6)

Strictly speaking the matrices Ul and Uq are independent up to a scalar phase factor that is negligible as compared to the phase difference due to the deterministic wavenumber mismatch.

The quantity that we refer to as the coherence length of the field describes the propagation distance along which the field decorrelates due to the fiber perturbations. It is not related to the coherence length of the light source.

The deterministic coupling between members of an LP mode group [9] is not included in B as its effect is assumed to be masked by the presence of the random perturbations which are represented by the second term in the square brackets of Eq. (1). This is consistent with the fact that strong random coupling between the constituent pseudo-modes is observed in experiments.

Figures (1)

(a) Average energy coupled from non-degenerate group q to a two-fold degenerate group l versus propagation distance normalized to Lc. The solid black line represents the complete expression given by Eq. (7), whereas the thin red and the dotted green lines were obtained in simulation with different parameters (see text). The dashed black line shows the simplified crosstalk expression given by Eq. (8). The shaded area marks one standard deviation from the mean as given by Eq. (9). (b) Standard deviation of the crosstalk σulq as obtained from Eq. (9) (thick-black curve) and from numerical simulations (thin red). (c) Crosstalk probability density function (circles) and chi-squared distribution fit (solid line).